Methods for branching pha using thermolysis

ABSTRACT

Branched PHA compositions, and related methods and articles are disclosed.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.61/133,026, filed on Jun. 25, 2008; 61/207,493, filed Feb. 12, 2009;61/133,023, filed on Jun. 25, 2008; 61/199,817, filed on Nov. 20, 2008;61/200,619 filed Dec. 2, 2008; 61/203,542 filed Dec. 23, 2008 and61/166,950 filed Apr. 6, 2009. The entire teachings of the aboveapplications are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to methods of making branchedpolyhydroxyalkanoate (PHA) compositions. The methods described hereinproduce more efficient branching, use less branching agent, and resultin lower amounts of odiferous decomposition residues in the finishedbranched PHA polymer. The compositions of branched PHA are useful inapplications such as thermoforming, particularly in thermoformeddisposable products such as utensils, tubs, bowls, lids, cup lids,yogurt cups, containers, bottles and bottle-like containers, and othercontainer-type items, foams, films, blown films, coatings and the like.

BACKGROUND

Biodegradable plastics are of increasing industrial interest asreplacements or supplements for non-biodegradable plastics in a widerange of applications and in particular for packaging applications. Oneclass of biodegradable polymers is the polyhydroxyalkanoates (PHAs),which are linear, aliphatic polyesters that can be produced by numerousmicroorganisms for use as intracellular storage material. Articles madefrom the polymers are generally recognized by soil microbes as a foodsource. There has therefore been a great deal of interest in thecommercial development of these polymers, particularly for disposableconsumer items. The polymers exhibit good biodegradability and usefulphysical properties.

Molecular weight, molecular weight distribution, short and long chainbranching are the dominating factors influencing processing and keyphysical properties of any polymeric composition. With molecular weightsbelow certain threshold values it also becomes impossible to providegood melt strength and to achieve required physical properties, e.g.,tensile strength or impact resistance.

PHA polymers have quite limited thermal stability, and undergo chainscission by beta-elimination mechanisms at general processingtemperatures and conditions. This can reduce the molecular weight quitesignificantly, and can result in resins with lower than requiredmolecular weights leaving manufacturing or the compounding floor.Commercial utility of PHAs also can be limited in some applications,such as films, coatings and thermoforming, because of the low meltstrength or melt elasticity often found in linear polymers. Thus, a needexists to address these shortcomings.

SUMMARY

Disclosed herein are methods of branching polyhydroxyalkanoate (PHA)polymers, by first thermolysing the PHA, and then reacting thethermolysed PHA with a branching agent, such as a peroxide. As usedherein, “branched PHA” refers to PHA polymer molecule containing longchain polymers comprising additional polymer chains pendant to orconnected to the long chain. Branching on branching via further sidechain polymers is also contemplated. This invention also relates toarticles, in particular, thermoformed articles made from the branchedpolymer compositions produced by the methods of the invention.

In one aspect, this invention features a method that includesthermolysing a starting PHA to reduce the molecular weight in a range of25% to 75% from its starting molecular weight and then reacting thethermolysed PHA with a branching agent (e.g., a free radical initiator,such as peroxide) at a temperature and time sufficient to inducebranching. In certain embodiments, the branching agent has a half-lifeof one third of the reaction time. In particular embodiments, thestarting or initial PHA is linear. In still other embodiments, theinitial or starting PHA is branched.

The branching methods described herein are useful for providing PHAswith desirable mechanical properties such as melt strength The methodsdescribed herein produce compositions containing branched PHA with anincreased melt strength compared to the starting PHA. Increasing themelt strength of PHAs is achieved by free-radical-induced cross-linkingor branching of the polymer. In one embodiment, the melt strength of thebranched PHA greater that 2-20 times the melt strength of the startingpolymer when measured at 160° C. and 0.25 rad/sec by torsional meltrheometry.

The resultant branched PHA compositions produced by the methodsdescribed herein are processed alone or in combination with PHAs orother materials by a range of polymer processing techniques includinginjection molding, cast film, cast sheet, thermoforming, blown film,blow molding, foam, fiber spinning or extrusion coating, onto asubstrate to form articles. In the case of extrusion coating, preferredsubstrates are paper or paper board. The branched PHA can also beproduced as a pellet for further processing.

The article can be, for example, a film, e.g., a blown film, a blowmolded article, a thermoformed article, a profile extruded article, afiber or a non-woven, a foam product, a coated paper product or a coatedpaperboard product. The product can be a polymer sheet suitable for usein thermoforming articles. The thermoformed product can be for example,a yogurt cup, a bowl, a lid, a cup lid and the like. In certainpreferred embodiments, a thermoformed article is produced using thebranched PHA made by the methods described herein.

In any of the methods, articles, or branched PHAs disclosed herein, thebranched PHAs can include one or more of the following features.

The branched PHA can have a melt strength of, for example, 2-10 timesgreater that the starting PHA, such as at 3-15 times greater, or 5-10times greater.

The branched PHA can have a polydispersity (PD) index greater than thestarting PHA.

The branched PHA is characterized by an weight average molecular weightthat is at least 1.2 times greater than the weight average molecularweight of the original PHA (herein designated as Mw/Mw,o). Morepreferably, Mw/Mw,o is at least 1.5 and most preferably at least 2.0.The practical upper limit of Mw/Mw,o is at the limit of polymer gelformation, which can act as imperfections in the PHA formulation. Theupper limit of Mw/Mw,o depends on the starting Mw,o in that highmolecular weight chains have a greater propensity to form gels. Thus, asthe Mw,o increases, the upper limit of Mw/Mw,o will be less. In mostcases, the upper limit of Mw/Mw,o is 4.0, more preferably 3.5 and mostpreferably 3.0.

The synthesis of the branched PHA composition can use a range of 0.001%to 0.5%, for example, 0.2 wt % of a free-radical initiator, or 0.05 wt %free radical initiator of the polymer composition. Alternatively, arange of 0.001% to 0.1% weight is useful.

After synthesis of the branched PHA, the branching agent is essentiallyall decomposed resulting in a branched PHA containing little or noresidual branching agent. The branching agent can be an organicperoxide. Examples of a suitable peroxide include but are not limited todicumyl peroxide, t-amyl-2-ethylhexyl peroxycarbonate,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-bis(t-butylperoxy)-2,5-dimethylhexane,2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoylperoxide, di-t-amyl peroxide, t-butyl cumyl peroxide,n-butyl-4,4-bis(t-butylperoxy)valerate,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)-cyclohexane,2,2-di(t-butylperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate,2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate,t-butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate,t-amylperoxybenzoate, and di-t-butyldiperoxyphthalate.

The reaction temperature of the thermolysing can be, for example,between 190° C. to 250° C. or for example, thermolysed at a temperaturebetween 200° C. or to 220° C. before the branching reaction step.

The average residence time in the extruder for the reaction, is forexample, at least 5 s, at least 30 s, at least 120 s, or at least 240 s.

The choice of a branching agent is based on the experimental conditionsfor polymer processing and the appropriate branching agent is chosenaccording to the half life of the branching agent under this processingtemperature and conditions, the branching agent is chosen for a halflife according to the processing conditions,

The details of one or more embodiments of the invention are set forth inthe description below. Other features, objects, and advantages of theinvention will be apparent from the description and from the claims.

DETAILED DESCRIPTION

The invention provides methods of making branched polymers by firstthermolysing (heat treating) the starting PHA, and then subsequentlyreacting the starting PHA with a branching agent. As disclosed herein,it has been found that thermolysing a starting PHA polymer to breakmolecules produces a population of molecules with reactive groups on theends. The thermolysing proceeds at a temperature until the molecularweight is reduced, e.g., the molecular weight is reduced to between 25%and 75% of the starting PHA, and in a certain embodiments between 40%and 60%, and in other embodiments, the reduction is half of the startingmolecular weight. Subsequent reaction with a branching agent, e.g., afree radical initiator, such as a peroxide, creates radicals on thebackbone of the linear polymer, which then react, either with eachother, or under certain conditions, with the reactive groups on the endsof the thermolysed PHA. The result is a branched PHA, but with theadvantage that lower amounts of peroxide can be used, while stillobtaining the same level of branching before the peroxide is decomposedby the polymer processing temperatures.

Branched polyhydroxyalkanoates are desirable in that branching can beused to improve the melt strength of PHAs. Melt strength is arheological property that can be measured a number of ways. One measureis G′, the polymer storage modulus is measured at melt processingtemperatures.

Increased melt strength is useful in that it allows the polymers to beformed under a broader temperature range when processed. Broadertemperature ranges are desirable for different polymer applications.This property is useful in the production of blown film (i.e., inpreventing bubble collapse), thermoformed articles (i.e., preventing orreducing sheet sag during thermoforming), profile extruded articles(i.e., preventing or reducing sag), and foam (i.e., preventing orreducing cell collapse and collapse of the overall foam).

Physical properties and rheological properties of polymeric materialsdepend on the molecular weight distribution of the polymer. ProducingPHA with desired rheological properties is achieved by the methodsdescribed herein. As used herein, “molecular weight” of the polymer canbe calculated in a number of different ways. Unless otherwise indicated,“molecular weight,” as it is used herein, refers to weight averagemolecular weight.

“Number average molecular weight” (M_(a)) represents the arithmetic meanof the distribution, and is the sum of the products of the molecularweights of each fraction, multiplied by its mole fraction(ΣN_(i)/ΣN_(i)).

“Weight average molecular weight” (M_(w)) is the sum of the products ofthe molecular weight of each fraction, multiplied by its weight fraction(ΣN_(i)M_(i) ²/Σ_(i)M_(i)). M_(w) is generally greater than or equal toM_(n). One way of increasing the melt strength is by branching the PHApolymer as described by the methods herein. Branching of a starting PHAcan be done by exposure of the polymer to heat (e.g., thermolysing)followed by reacting the thermolysed PHA with a branching agents, e.g.,peroxides.

Polyhydroxyalkanoates (PHAs)

Polyhydroxyalkanoates are biological polyesters synthesized by a broadrange of natural and genetically engineered bacteria as well asgenetically engineered plant crops (Braunegg et al., (1998), J.Biotechnology 65: 127-161; Madison and Huisman, 1999, Microbiology andMolecular Biology Reviews, 63: 21-53; Poirier, 2002, Progress in LipidResearch 41: 131-155). These polymers are biodegradable thermoplasticmaterials, produced from renewable resources, with the potential for usein a broad range of industrial applications (Williams & Peoples,CHEMTECH 26:38-44 (1996)). Useful microbial strains for producing PHAs,include Alcaligenes eutrophus (renamed as Ralstonia eutropha),Alcaligenes latus, Azotobacter, Aeromonas, Comamonas, Pseudomonads, andgenetically engineered organisms including genetically engineeredmicrobes such as Pseudomonas, Ralstonia and Escherichia coli.

In general, a PHA is formed by enzymatic polymerization of one or moremonomer units inside a living cell. Over 100 different types of monomershave been incorporated into the PHA polymers (Steinbuchel and Valentin,1995, FEMS Microbiol. Lett. 128: 219-228. Examples of monomer unitsincorporated in PHAs include 2-hydroxybutyrate, lactic acid, glycolicacid, 3-hydroxybutyrate (hereinafter referred to as 3HB),3-hydroxypropionate (hereinafter referred to as 3HP), 3-hydroxyvalerate(hereinafter referred to as 3HV), 3-hydroxyhexanoate (hereinafterreferred to as 3HH), 3-hydroxyheptanoate (hereinafter referred to as3HHep), 3-hydroxyoctanoate (hereinafter referred to as 3HO),3-hydroxynonanoate (hereinafter referred to as 3HN), 3-hydroxydecanoate(hereinafter referred to as 3HD), 3-hydroxydodecanoate (hereinafterreferred to as 3HDd), 4-hydroxybutyrate (hereinafter referred to as4HB), 4-hydroxyvalerate (hereinafter referred to as 4HV),5-hydroxyvalerate (hereinafter referred to as 5HV), and6-hydroxyhexanoate (hereinafter referred to as 6HH). 3-hydroxyacidmonomers incorporated into PHAs are the (D) or (R) 3-hydroxyacid isomerwith the exception of 3HP which does not have a chiral center.

In some embodiments, the starting PHA for use in the methods describedherein can be a homopolymer (where all monomer units are the same).Examples of PHA homopolymers include poly 3-hydroxyalkanoates (e.g.,poly 3-hydroxypropionate (hereinafter referred to as P3HP), poly3-hydroxybutyrate (hereinafter referred to as PHB) and poly3-hydroxyvalerate), poly 4-hydroxyalkanoates (e.g., poly4-hydroxybutyrate (hereinafter referred to as P4HB), or poly4-hydroxyvalerate (hereinafter referred to as P4HV)) and poly5-hydroxyalkanoates (e.g., poly 5-hydroxyvalerate (hereinafter referredto as P5HV)).

In certain embodiments, the starting PHA can be a copolymer (containingtwo or more different monomer units) in which the different monomers arerandomly distributed in the polymer chain. Examples of PHA copolymersinclude poly 3-hydroxybutyrate-co-3-hydroxypropionate (hereinafterreferred to as PHB3HP), poly 3-hydroxybutyrate-co-4-hydroxybutyrate(hereinafter referred to as PHB4HB), poly3-hydroxybutyrate-co-4-hydroxyvalerate (hereinafter referred to asPHB4HV), poly 3-hydroxybutyrate-co-3-hydroxyvalerate (hereinafterreferred to as PHB3HV), poly 3-hydroxybutyrate-co-3-hydroxyhexanoate(hereinafter referred to as PHB3HH) and poly3-hydroxybutyrate-co-5-hydroxyvalerate (hereinafter referred to asPHB5HV).

By selecting the monomer types and controlling the ratios of the monomerunits in a given PHA copolymer a wide range of material properties canbe achieved. Although examples of PHA copolymers having two differentmonomer units have been provided, the PHA can have more than twodifferent monomer units (e.g., three different monomer units, fourdifferent monomer units, five different monomer units, six differentmonomer units). An example of a PHA having 4 different monomer unitswould be PHB-co-3HH-co-3HO-co-3HD or PHB-co-3-HO-co-3HD-co-3HDd (thesetypes of PHA copolymers are hereinafter referred to as PHB3HX).Typically where the PHB3HX has 3 or more monomer units the 3HB monomeris at least 70% by weight of the total monomers, preferably 85% byweight of the total monomers, most preferably greater than 90% by weightof the total monomers for example 92%, 93%, 94%, 95%, 96% by weight ofthe copolymer and the HX comprises one or more monomers selected from3HH, 3HO, 3HD, 3HDd.

The homopolymer (where all monomer units are identical) PHB and3-hydroxybutyrate copolymers (PHB3HP, PHB4HB, PHB3HV, PHB4HV, PHB5HV,PHB3HHP, hereinafter referred to as PHB copolymers) containing3-hydroxybutyrate and at least one other monomer are of particularinterest for commercial production and applications. It is useful todescribe these copolymers by reference to their material properties asfollows. Type 1 PHB copolymers typically have a glass transitiontemperature (Tg) in the range of 6° C. to −10° C., and a meltingtemperature T_(M) of between 80° C. to 180° C. Type 2 PHB copolymerstypically have a Tg of −20° C. to −50° C. and Tm of 55° C. to 90° C.

Preferred Type 1 PHB copolymers have two monomer units have a majorityof their monomer units being 3-hydroxybutyrate monomer by weight in thecopolymer, for example, greater than 78% 3-hydroxybutyrate monomer.Preferred PHB copolymers for this invention are biologically producedfrom renewable resources and are selected from the following group ofPHB copolymers:

-   -   PHB3HV is a Type 1 PHB copolymer where the 3HV content is in the        range of 3% to 22% by weight of the polymer and preferably in        the range of 4% to 15% by weight of the copolymer for example:        4% 3HV; 5% 3HV; 6% 3HV; 7% 3HV; 8% 3HV; 9% 3HV; 10% 3HV; 11%        3HV; 12% 3HV; 13% 3HV; 14% 3HV; and 15% 3HV.    -   PHB3HP is a Type 1 PHB copolymer where the 3-HP content is in        the range of 3% to 15% by weight of the copolymer and preferably        in the range of 4% to 15% by weight of the copolymer for        example: 4% 3HP; 5% 3HP; 6% 3HP; 7% 3HP; 8% 3HP; 9% 3HP; 10%        3HP; 11% 3HP; 12% 3HP; 13% 3HP; 14% 3HP and 15% 3HP.    -   PHB4HB is a Type 1 PHB copolymer where the 4HB content is in the        range of 3% to 15% by weight of the copolymer and preferably in        the range of 4% to 15% by weight of the copolymer for example:        4% 4HB; 5% 4HB; 6% 4HB; 7% 4HB; 8% 4HB; 9% 4HB; 10% 4HB; 11%        4HB; 12% 4HB; 13% 4HB; 14% 4HB; and 15% 4HB.    -   PHB4HV is a Type 1 PHB copolymer where the 4HV content is in the        range of 3% to 15% by weight of the copolymer and preferably in        the range of 4% to 15% by weight of the copolymer for example:        4% 4HV; 5% 4HV; 6% 4HV; 7% 4HV; 8% 4HV; 9% 4HV; 10% 4HV; 11%        4HV; 12% 4HV; 13% 4HV; 14% 4HV; 15% 4HV.    -   PHB5HV is a Type 1 PHB copolymer where the 5HV content is in the        range of 3% to 15% by weight of the copolymer and preferably in        the range of 4% to 15% by weight of the copolymer for example:        4% 5HV; 5% 5HV; 6% 5HV; 7% 5HV; 8% 5HV; 9% 5HV; 10% 5HV; 11%        5HV; 12% 5HV; 13% 5HV; 14% 5 HV; 15% 5HV.    -   PHB3HH is a Type 1 PHB copolymer where the 3HH content is in the        range of 3% to 15% by weight of the copolymer and preferably in        the range of 4% to 15% by weight of the copolymer for example:        4% 3HH; 5% 3HH; 6% 3HH; 7% 3HH; 8% 3HH; 9% 3HH; 10% 3HH; 11%        3HH; 12% 3HH; 13% 3HH; 14% 3HH; 15% 3HH;    -   PHB3HX is a Type 1 PHB copolymer where the 3HX content is        comprised of 2 or more monomers selected from 3HH, 3HO, 3HD and        3HDd and the 3HX content is in the range of 3% to 12% by weight        of the copolymer and preferably in the range of 4% to 10% by        weight of the copolymer for example: 4% 3HX; 5% 3HX; 6% 3HX; 7%        3HX; 8% 3HX; 9% 3HX; 10% 3HX by weight of the copolymer.    -   Type 2 PHB copolymers have a 3HB content of between 80% and 5%        by weight of the copolymer, for example 80%, 75%, 70%, 65%, 60%,        55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%,10% by weight of the        copolymer.    -   PHB4HB is a Type 2 PHB copolymer where the 4HB content is in the        range of 20% to 60% by weight of the copolymer and preferably in        the range of 25% to 50% by weight of the copolymer for example:        25% 4HB; 30% 4HB; 35% 4HB; 40% 4HB; 45% 4HB; 50% 4HB by weight        of the copolymer.    -   PHB5HV is a Type 2 PHB copolymer where the 5HV content is in the        range of 20% to 60% by weight of the copolymer and preferably in        the range of 25% to 50% by weight of the copolymer for example:        25% 5HV; 30% 5HV; 35% 5HV; 40% 5HV; 45% 5HV; 50% 5HV by weight        of the copolymer.    -   PHB3HH is a Type 2 PHB copolymer where the 3HH is in the range        of 35% to 95% by weight of the copolymer and preferably in the        range of 40% to 80% by weight of the copolymer for example: 40%        3HH; 45% 3HH; 50% 3HH; 55% 3HH 60% 3HH; 65% 3HH; 70% 3HH; 75%        3HH; 80% 3HH by weight of the copolymer.    -   PHB3HX is a Type 2 PHB copolymer where the 3HX content is        comprised of 2 or more monomers selected from 3HH, 3HO, 3HD and        3HDd and the 3HX content is in the range of 30% to 95% by weight        of the copolymer and preferably in the range of 35% to 90% by        weight of the copolymer for example: 35% 3HX; 40% 3HX; 45% 3HX;        50% 3HX; 55% 3HX; 60% 3HX; 65% 3HX; 70% 3HX; 75% 3HX; 80% 3HX;        85% 3HX; 90% 3HX; by weight of the copolymer.

PHAs for use in the methods, compositions and pellets described in thisinvention are selected from : PHB or a Type 1 PHB copolymer; a PHA blendof PHB with a Type 1 PHB copolymer where the PHB content by weight ofPHA in the PHA blend is in the range of 5% to 95% by weight of the PHAin the PHA blend; a PHA blend of PHB with a Type 2 PHB copolymer wherethe PHB content by weight of the PHA in the PHA blend is in the range of5% to 95% by weight of the PHA in the PHA blend; a PHA blend of a Type 1PHB copolymer with a different Type 1 PHB copolymer and where thecontent of the first Type 1 PHB copolymer is in the range of 5% to 95%by weight of the PHA in the PHA blend; a PHA blend of a Type 1 PHBcopolymer with a Type 2 PHA copolymer where the content of the Type 1PHB copolymer is in the range of 30% to 95% by weight of the PHA in thePHA blend; a PHA blend of PHB with a Type 1 PHB copolymer and a Type 2PHB copolymer where the PHB content is in the range of 10% to 90% byweight of the PHA in the PHA blend, where the Type 1 PHB copolymercontent is in the range of 5% to 90% by weight of the PHA in the PHAblend and where the Type 2 PHB copolymer content is in the range of 5%to 90% by weight of the PHA in the PHA blend.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHBP3HP where the PHB content in the PHA blend is in the range of5% to 90% by weight of the PHA in the PHA blend and the 3HP content inthe PHBP3HP is in the range of 7% to 15% by weight of the PHBP3HP.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB3HV where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 3HV content in thePHB3HV is in the range of 4% to 22% by weight of the PHB3HV.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB4HB where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 4HB content in thePHB4HB is in the range of 4% to 15% by weight of the PHB4HB.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB4HV where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 4HV content in thePHB4HV is in the range of 4% to 15% by weight of the PHB4HV.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB5HV where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 5HV content in thePHB5HV is in the range of 4% to 15% by weight of the PHB5HV.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB3HH where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 3HH content in thePHB3HH is in the range of 4% to 15% by weight of the PHB3HH.

The PHA blend of PHB with a Type 1 PHB copolymer can be a blend of PHBwith PHB3HX where the PHB content of the PHA blend is in the range of 5%to 90% by weight of the PHA in the PHA blend and the 3HX content in thePHB3HX is in the range of 4% to 15% by weight of the PHB3HX.

The PHA blend can be a blend of a Type 1 PHB copolymer selected from thegroup PHB3HV, PHB3HP, PHB4HB, PHBV, PHV4HV, PHB5HV, PHB3HH and PHB3HXwith a second Type 1 PHB copolymer which is different from the firstType 1 PHB copolymer and is selected from the group PHB3HV, PHB3HP,PHB4HB, PHBV, PHV4HV, PHB5HV, PHB3HH and PHB3HX where the content of theFirst Type 1 PHB copolymer in the PHA blend is in the range of 10% to90% by weight of the total PHA in the blend.

The PHA blend of PHB with a Type 2 PHB copolymer can be a blend of PHBwith PHB4HB where the PHB content in the PHA blend is in the range of30% to 95% by weight of the PHA in the PHA blend and the 4HB content inthe PHB4HB is in the range of 20% to 60% by weight of the PHB4HB.

The PHA blend of PHB with a Type 2 PHB copolymer can be a blend of PHBwith PHB5HV where the PHB content in the PHA blend is in the range of30% to 95% by weight of the PHA in the PHA blend and the 5HV content inthe PHB5HV is in the range of 20% to 60% by weight of the PHB5HV.

The PHA blend of PHB with a Type 2 PHB copolymer can be a blend of PHBwith PHB3HH where the PHB content in the PHA blend is in the range of35% to 95% by weight of the PHA in the PHA blend and the 3HH content inthe PHB3HH is in the range of 35% to 90% by weight of the PHB3HX.

The PHA blend of PHB with a Type 2 PHB copolymer can be a blend of PHBwith PHB3HX where the PHB content in the PHA blend is in the range of30% to 95% by weight of the PHA in the PHA blend and the 3HX content inthe PHB3HX is in the range of 35% to 90% by weight of the PHB3HX.

The PHA blend can be a blend of PHB with a Type 1 PHB copolymer and aType 2 PHB copolymer where the PHB content in the PHA blend is in therange of 10% to 90% by weight of the PHA in the PHA blend, the Type 1PHB copolymer content of the PHA blend is in the range of 5% to 90% byweight of the PHA in the PHA blend and the Type 2 PHB copolymer contentin the PHA blend is in the range of 5% to 90% by weight of the PHA inthe PHA blend.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HVcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HV content in the PHB3HV is in the range of 3%to 22% by weight of the PHB3HV, and a PHBHX content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the3HX content in the PHBHX is in the range of 35% to 90% by weight of thePHBHX.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HVcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HV content in the PHB3HV is in the range of 3%to 22% by weight of the PHB3HV, and a PHB4HB content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the4HB content in the PHB4HB is in the range of 20% to 60% by weight of thePHB4HB.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HVcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HV content in the PHB3HV is in the range of 3%to 22% by weight of the PHB3HV, and a PHB5HV content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the5HV content in the PHB5HV is in the range of 20% to 60% by weight of thePHB5HV.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB4HBcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 4HB content in the PHB4HB is in the range of 4%to 15% by weight of the PHB4HB, and a PHB4HB content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the4HB content in the PHB4HB is in the range of 20% to 60% by weight of thePHB4HB.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB4HBcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 4HB content in the PHB4HB is in the range of 4%to 15% by weight of the PHB4HB, and a PHB5HV content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend and wherethe 5HV content in the PHB5HV is in the range of 30% to 90% by weight ofthe PHB5HV.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB4HBcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 4HB content in the PHB4HB is in the range of 4%to 15% by weight of the PHB4HB, and a PHB3HX content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend and wherethe 3HX content in the PHB3HX is in the range of 35% to 90% by weight ofthe PHB3HX.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB4HVcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 4HV content in the PHB4HV is in the range of 3%to 15% by weight of the PHB4HV, and a PHB5HV content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the5HV content in the PHB5HV is in the range of 30% to 90% by weight of thePHB5HV.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HHcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HH content in the PHB3HH is in the range of 3%to 15% by weight of the PHB3HH, and a PHB4HB content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the4HB content in the PHB4HB is in the range of 20% to 60% by weight of thePHB4HB.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HHcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HH content in the PHB3HH is in the range of 3%to 15% by weight of the PHB3HH, and a PHB5HV content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the5HV content in the PHB5HV is in the range of 20% to 60% by weight of thePHB5HV.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HHcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HH content in the PHB3HH is in the range of 3%to 15% by weight of the PHB3HH, and a PHB3HX content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the3HX content in the PHB3HX is in the range of 35% to 90% by weight of thePHB3HX.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HXcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HX content in the PHB3HX is in the range of 3%to 12% by weight of the PHB3HX, and a PHB3HX content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the3HX content in the PHB3HX is in the range of 35% to 90% by weight of thePHB3HX.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HXcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HX content in the PHB3HX is in the range of 3%to 12% by weight of the PHB3HX, and a PHB4HB content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the4HB content in the PHB4HB is in the range of 20% to 60% by weight of thePHB4HB.

For example a PHA blend can have a PHB content in the PHA blend in therange of 10% to 90% by weight of the PHA in the PHA blend, a PHB3HXcontent in the PHA blend in the range 5% to 90% by weight of the PHA inthe PHA blend, where the 3HX content in the PHB3HX is in the range of 3%to 12% by weight of the PHB3HX, and a PHB5HV content in the PHA blend inthe range of 5% to 90% by weight of the PHA in the PHA blend where the5HV content in the PHB5HV is in the range of 20% to 60% by weight of thePHB5HV.

The PHA blend can be a blend as disclosed in U.S. Pub. App. No.2004/0220355, by Whitehouse, published Nov. 4, 2004, which isincorporated herein by reference in its entirety.

Microbial systems for producing the PHB copolymer PHBV are disclosed inU.S. Pat. No. 4,477,654 to Holmes. U.S. Pat. App. Pub 2002/0164729, bySkraly and Sholl describes useful systems for producing the PHBcopolymer PHB4HB. Useful processes for producing the PHB copolymerPHB3HH have been described (Lee et al., 2000, Biotechnology andBioengineering 67: 240-244; Park et al., 2001, Biomacromolecules, 2:248-254). Processes for producing the PHB copolymers PHB3HX have beendescribed by Matsusaki et al., (Biomacromolecules, 2000, 1: 17-22).

In determining the molecular weight techniques such as gel permeationchromatography (GPC) can be used. In the methodology, a polystyrenestandard is utilized. The PHA can have a polystyrene equivalent weightaverage molecular weight (in daltons) of at least 500, at least 10,000,or at least 50,000 and/or less than 2,000,000, less than 1,000,000, lessthan 1,500,000, and less than 800,000. In certain embodiments,preferably, the PHAs generally have a weight-average molecular weight inthe range of 100,000 to 700,000. For example, the molecular weight rangefor PHB and Type 1 PHB copolymers for use in this application are in therange of 400,000 daltons to 1.5 million daltons as determined by GPCmethod and the molecular weight range for Type 2 PHB copolymers for usein the application 100,000 to 1.5 million daltons.

In certain embodiments, the branched PHA can have a linear equivalentweight average molecular weight of from about 150,000 Daltons to about500,000 Daltons and a polydispersity index of from about 2.5 to about8.0. As used herein, weight average molecular weight and linearequivalent weight average molecular weight are determined by gelpermeation chromatography, using, e.g., chloroform as both the eluentand diluent for the PHA samples. Calibration curves for determiningmolecular weights are generated using linear polystyrenes as molecularweight standards and a ‘log MW vs elution volume’ calibration method.

Production of Branched PHA

The branching agents for use in the compositions and method describedherein include branching agents, also referred to as free radicalinitiators, e.g., organic peroxides. Peroxides are reactive molecules,and can react with linear PHA molecules or previously branched PHA byremoving a hydrogen atom from the polymer backbone or side chainbackbone, leaving behind a radical. PHA molecules having such radicalson their backbones are free to combine with each other, creatingbranched PHA molecules.

When peroxides decompose at processing temperatures, they producedecomposition products and residues, many of which produce noxious odorsin the finished polymer. Such odors are unappealing to consumers. In theproduction of other branched polymers, such as polypropylene, this isless of a problem because branched polypropylene is typically producedat temperatures of 200° C. to 250° C., and the by-products are morereadily removed. Polyhydroxyalkanoates, however, are processed at muchlower temperatures, and so the by-products are not as efficientlyremoved. It is therefore desirable to use as little peroxide as possiblewhen producing branched PHAs.

Disclosed herein is a two-step method of branching PHA. It has beenfound that more efficient branching can be induced inpolyhydroxyalkanoate polymers by first thermolysing (i.e., heattreating) the PHA, and then subsequently treating it with a branchingagent. This allows less peroxide to be used to achieve branching,thereby reducing the level of undesirable peroxide decompositionproducts.

During thermolysis, the polyhydroxyalkanoate polymer chains are cleaved,resulting in unsaturated end groups. This thermolysed polymer, withunsaturated end groups, is then reacted with one or more branchingagents, such as peroxides. The peroxides remove hydrogen atoms from thepolymer backbones, and the resulting radicals are free to react not onlywith each other, but also the reactive groups on the ends of the PHAthat were produced during thermolysis. The result is more efficientbranching, because each peroxide-produced radical can not only reactwith another peroxide produced radical but can also react with the chainend.

For instance, the PHA polymer can be thermolysed, and its molecularweight reduced, for example, by 25% to 75%, by 40% to 60%, or by 50%. Abranching agent, e.g., a peroxide, can then be used to branch thepolymer and bond multiple polymer molecules together. This is shown inthe examples below. Also contemplated is using a starting branchedpolymer.

In certain embodiments, the branched PHA can be prepared as follows.First a PHA is thermolysed (heat treated) at elevated temperature tobreak the polymer chains. For example, a PHA (either linear or branched)is heated at an elevated temperature (e.g., from 170° C. to about 220°C., or from about 190° C. to about 220° C. for a sufficient period oftime (e.g., from 0.5 minutes to 3.0 minutes) before it is mixed with afree radical initiator. Typically, this temperature is higher than thetemperature used in the subsequent branching reaction. Without wishingto be bound by any theory, it is believed that certain PHA polymerchains are cleaved during the thermal treatment and terminal reactivegroups are produced (during the subsequent branching reaction, theseterminal reactive groups will facilitate the formation of branching byreacting with radical sites on other PHA molecules which are formed whenthe free radical initiator is added to the polymer). As a result of thischain cleavage, the thermally treated PHA has a lower weight averagemolecular weight than it did before heat treatment.

Because the thermally treated PHA (e.g., thermolysed PHA) alreadycontains terminal reactive groups when the branching initiator is added,this method can be used to prepare PHAs with a high degree of branching.

The thermolysed PHA is then mixed with the requisite quantity of a freeradical initiator by a suitable means. The mixing step can preferably becarried out under the conditions that the initiator does not undergosubstantial decomposition. The branching reaction is then carried out byexposing the mixture to a temperature above the melting temperature ofthe PHA and the decomposition temperature of the initiator for asufficient period of time. Without wishing to be bound by any theory, itis believed that decomposition of the initiator forms free radicals,which react with PHA molecules to generate radical sites on the polymerbackbone. A branched PHA can then be formed by a coupling reactionbetween these radical sites on PHA molecules with other such radicalsites, or the reactive groups at the broken ends of the linear moleculesthat were created during the thermolysis step.

Typically, the reaction time is sufficient for branching between polymermolecules while substantially all of the branching agent decompose. Forexample, the reaction time should at least three times the half-life ofthe initiator at the reaction temperature. The branched PHA thusprepared contains a minimal amount of residual initiator and possessesimproved stability and reproducibility. Typically, the branched PHA hasa higher degree of branching and weight average molecular weight thanthe initial PHA. For example, the branched PHA can have a weight averagemolecular weight of least about 1.2 times as high as that of the linearPHA. The branched PHA has a G′ of about 2 to 20 times that of thestarting PHA.

Both the thermolysis step and the branching reaction are performed astwo separate steps, for example, the PHA can be thermolysed andextruded, and then combined with the branching agent in a separate run.

Alternatively, both steps can be performed in a single extruder indifferent subsequent zones. For instance, the thermolysing step can bedone in an extruder, and when the PHA is sufficiently thermolysed, thebranching agent may be added to conduct the branching step. That is, thethermolysing step and the branching step are separate in time.

Both steps can also be performed in separate zones in the extruder. Forinstance, the thermolysis step can be performed in one zone of anextruder, and the branching agent can then be added as the thermolysedPHA enters another zone of the extruder.

Branching Agents

Branching agents also referred to as free radical initiators areselected from any suitable initiator known in the art, such as organicperoxides, azo-dervatives (e.g., azo-nitriles), peresters, andperoxycarbonates. Suitable peroxides for use in the present inventioninclude, but are not limited to, organic peroxides, for example dialkylorganic peroxides such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-bis(t-butylperoxy)-2,5-dimethylhexane (available from Akzo Nobel asTRIGANOX 101), tert-butylperoxy-2-ethylhexylcarbonate (available fromAkzo Nobel as TRIGANOX 117), tert-amylperoxy-2-ethylhexylcarbonate(available from Akzo Nobel as TRIGANOX 131),n-butyl-4,4-di-(tert-butylperoxy)valerate (available from Akzo Nobel asTRIGANOX 17), 2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butylperoxide, dicumyl peroxide (DCP, DiCuP), benzoyl peroxide, di-t-amylperoxide, t-amylperoxy-2-ethylhexylcarbonate (TAEC),t-butyl-2-ethylhexyl peroxycarbonate, t-butyl cumyl peroxide,n-butyl-4,4-bis(t-butylperoxy)valerate,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane (CPK),1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)-cyclohexane,2,2-di(t-butylperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate,2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate,t-butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate(TBPB), t-amylperoxybenzoate, di-t-butyldiperoxyphthalate, and the like.Combinations and mixtures of peroxides can also be used. Examples offree radical initiators include those mentioned herein, as well as thosedescribed in, e.g., Polymer Handbook, 3^(rd) Ed., J. Brandrup & E. H.Immergut, John Wiley and Sons, 1989, Ch. 2. Irradiation (e.g., e-beam orgamma irradiation) can also be used to generate PHA branching.

Additives

In certain embodiments, various additives is added to the branched PHAdescribed above. Examples of these additives include antioxidants,pigments, UV stabilizers, fillers, plasticizers, nucleating agents, andradical scavengers.

Optionally, an additive is included in the thermoplastic composition.The additive is any compound known to those of skill in the art to beuseful in the production of thermoplastics. Exemplary additives include,e.g., plasticizers (e.g., to increase flexibility of a thermoplasticcomposition), antioxidants (e.g., to protect the thermoplasticcomposition from degradation by ozone or oxygen), ultravioletstabilizers (e.g., to protect against weathering), lubricants (e.g., toreduce friction), pigments (e.g., to add color to the thermoplasticcomposition), flame retardants, fillers, reinforcing, mold release, andantistatic agents. It is well within the skilled practitioner'sabilities to determine whether an additive should be included in athermoplastic composition and, if so, what additive and the amount thatshould be added to the composition.

In poly-3-hydroxybutyrate compositions, for example, plasticizers areoften used to change the glass transition temperature and modulus of thecomposition, but surfactants may also be used. Lubricants may also beused, e.g., in injection molding applications. Plasticizers, surfactantsand lubricants may all therefore be included in the overall blend. Incertain embodiments, the compositions and methods of the inventioninclude one or more surfactants. Surfactants are generally used tode-dust, lubricate, reduce surface tension, and/or densify.

One or more lubricants can also be added to the compositions and methodsof the invention Lubricants are normally used to reduce sticking to hotprocessing metal surfaces and can include polyethylene, paraffin oils,and paraffin waxes in combination with metal stearates. Other lubricantsinclude stearic acid, amide waxes, ester waxes, metal carboxylates, andcarboxylic acids. Lubricants are normally added to polymers in the rangeof about 0.1 percent to about 1 percent by weight, generally from about0.7 percent to about 0.8 percent by weight of the compound. Solidlubricants is warmed and melted before or during processing of theblend.

Nucleating Agents

For instance, an optional nucleating agent is added to the branched PHAto aid in its crystallization. Nucleating agents for various polymersare simple substances, metal compounds including composite oxides, forexample, carbon black, calcium carbonate, synthesized silicic acid andsalts, silica, zinc white, clay, kaolin, basic magnesium carbonate,mica, talc, quartz powder, diatomite, dolomite powder, titanium oxide,zinc oxide, antimony oxide, barium sulfate, calcium sulfate, alumina,calcium silicate, metal salts of organophosphates, and boron nitride;low-molecular organic compounds having a metal carboxylate group, forexample, metal salts of such as octylic acid, toluic acid, heptanoicacid, pelargonic acid, lauric acid, myristic acid, palmitic acid,stearic acid, behenic acid, cerotic acid, montanic acid, melissic acid,benzoic acid, p-tert-butylbenzoic acid, terephthalic acid, terephthalicacid monomethyl ester, isophthalic acid, and isophthalic acid monomethylester; high-molecular organic compounds having a metal carboxylategroup, for example, metal salts of such as: carboxyl-group-containingpolyethylene obtained by oxidation of polyethylene;carboxyl-group-containing polypropylene obtained by oxidation ofpolypropylene; copolymers of olefins, such as ethylene, propylene andbutene-1, with acrylic or methacrylic acid; copolymers of styrene withacrylic or methacrylic acid; copolymers of olefins with maleicanhydride; and copolymers of styrene with maleic anhydride;high-molecular organic compounds, for example: alpha-olefins branched attheir 3-position carbon atom and having no fewer than 5 carbon atoms,such as 3,3dimethylbutene-1,3-methylbutene-1,3-methylpentene-1,3-methylhexene-1,and 3,5,5-trimethylhexene-1; polymers of vinylcycloalkanes such asvinylcyclopentane, vinylcyclohexane, and vinylnorbornane; polyalkyleneglycols such as polyethylene glycol and polypropylene glycol;poly(glycolic acid); cellulose; cellulose esters; and cellulose ethers;phosphoric or phosphorous acid and its metal salts, such as diphenylphosphate, diphenyl phosphite, metal salts ofbis(4-tert-butylphenyl)phosphate, and methylenebis-(2,4-tert-butylphenyl)phosphate; sorbitol derivatives such asbis(p-methylbenzylidene) sorbitol and bis(p-ethylbenzylidene) sorbitol;and thioglycolic anhydride, p-toluenesulfonic acid and its metal salts.The above nucleating agents may be used either alone or in combinationswith each other. In particular embodiments, the nucleating agent iscyanuric acid. In certain embodiments, the nucleating agent can also beanother polymer (e.g., polymeric nucleating agents such as PHB).

In certain embodiments, the nucleating agent is selected from: cyanuricacid, carbon black, mica talc, silica, boron nitride, clay, calciumcarbonate, synthesized silicic acid and salts, metal salts oforganophosphates, and kaolin. In particular embodiments, the nucleatingagent is cyanuric acid.

In various embodiments, where the nucleating agent is dispersed in aliquid carrier, the liquid carrier is a plasticizer, e.g., a citriccompound or an adipic compound, e.g., acetylcitrate tributyrate(Citroflex A4, Vertellus, Inc., High Point, N.C.), or DBEEA(dibutoxyethoxyethyl adipate), a surfactant, e.g., Triton X-100,TWEEN-20, TWEEN-65, Span-40 or Span 85, a lubricant, a volatile liquid,e.g., chloroform, heptane, or pentane, a organic liquid or water.

In other embodiments, the nucleating agent is aluminum hydroxydiphosphate or a compound comprising a nitrogen-containingheteroaromatic core. The nitrogen-containing heteroaromatic core ispyridine, pyrimidine, pyrazine, pyridazine, triazine, or imidazole.

In particular embodiments, the nucleating agent can include aluminumhydroxy diphosphate or a compound comprising a nitrogen-containingheteroaromatic core. The nitrogen-containing heteroaromatic core ispyridine, pyrimidine, pyrazine, pyridazine, triazine, or imidazole. Thenucleant can have a chemical formula selected from the group consistingof

and combinations thereof, wherein each R1 is independently H, NR²R²,OR², SR², SOR², SO₂R², CN, COR², CO₂R², CONR²R², NO₂, F, Cl, Br, or I;and each R² is independently H or C₁-C₆ alkyl.

Another nucleating agent for use in the compositions and methodsdescribed herein are milled as described in PCT/US2009/041023, filedApr. 17, 2009, which is incorporated by reference in its entirety.Briefly, the nucleating agent is milled in a liquid carrier until atleast 5% of the cumulative solid volume of the nucleating agent existsas particles with a particle size of 5 microns or less. The liquidcarrier allows the nucleating agent to be wet milled. In otherembodiments, the nucleating agent is milled in liquid carrier until atleast 10% of the cumulative solid volume, at least 20% of the cumulativesolid volume, at least 30% or at least 40%-50% of the nucleating agentcan exist as particles with a particle size of 5 microns or less, 2microns or less or 1 micron or less. In alternative embodiments, thenucleating agents is milled by other methods, such as jet milling andthe like. Additionally, other methods is utilized that reduce theparticle size.

The cumulative solid volume of particles is the combined volume of theparticles in dry form in the absence of any other substance. Thecumulative solid volume of the particles is determined by determiningthe volume of the particles before dispersing them in a polymer orliquid carrier by, for example, pouring them dry into a graduatedcylinder or other suitable device for measuring volume. Alternatively,cumulative solid volume is determined by light scattering.

Applications for Branched Polymers

The branched PHA compositions and produced by the methods describedherein can be used to create, without limitation, a wide variety ofuseful products, e.g., automotive, consumer durable, construction,electrical, medical, and packaging products. For instance, the polymericcompositions can be used to make, without limitation, films (e.g.,packaging films, agricultural film, mulch film, erosion control, haybale wrap, slit film, food wrap, pallet wrap, protective automobile andappliance wrap, etc.), golf tees, caps and closures, agriculturalsupports and stakes, paper and board coatings (e.g., for cups, plates,boxes, etc.), thermoformed products (e.g., trays, containers, lids,yoghurt pots, cup lids, plant pots, noodle bowls, moldings, etc.),housings (e.g., for electronics items, e.g., cell phones, PDA cases,music player cases, computer cases and the like), bags (e.g., trashbags, grocery bags, food bags, compost bags, etc.), hygiene articles(e.g., diapers, feminine hygiene products, incontinence products,disposable wipes, etc.), coatings for pelleted products (e.g., pelletedfertilizer, herbicides, pesticides, seeds, etc.), injection moldings(writing instruments, utensils, disk cases, etc.), solution and spunfibers and melt blown fabrics and non-wovens (threads, yarns, wipes,wadding, disposable absorbent articles, etc.), blow moldings (deepcontainers, bottles, etc.) and foamed articles (cups, bowls, plates,packaging, etc.).

Thermoforming is a process that that uses films or sheets ofthermoplastic. The polymeric composition made by the methods herein isprocessed into a film or sheet. The sheet of polymer is then placed inan oven and heated. When soft enough to be formed, the sheet istransferred to a mold, formed and shaped.

During thermoforming, when the softening point of a semi-crystallinepolymer is reached, the polymer sheet begins to sag. The window betweensoftening and droop is usually narrow. It can therefore be difficult tomove the softened polymer sheet to the mold quickly enough. Branchingthe polymer as described herein increases melt strength of the polymerso that the sheet is more readily processed and maintains its structuralintegrity. Measuring the sag of a sample piece of polymer when it isheated is therefore a way to measure the relative size of thisprocessing window for thermoforming.

Because the branched polymers described herein have increased meltstrength and increased processability, they are easier to convert tofilm or sheet form. They are therefore excellent candidates forthermoforming. Molded products can include a number of different producttypes and, for example, can include products such as disposable spoons,forks and knives, tubs, bowls, lids, cup lids, yogurt cups, and othercontainers, bottles and bottle-like containers, etc.

Blow molding, which is similar to thermoforming and is used to producedeep draw products such as bottles and similar products with deepinteriors, also benefits from the increased elasticity and melt strengthand reduced sag of the branched polymer compositions described herein.

The branched PHA compositions described herein can be provided in anysuitable form convenient for an intended application. For example,branched PHA can be provided in pellet for to subsequently producefilms, coatings, moldings or other articles, or the films, coatings,moldings and other articles can be made directly as the branched PHA isproduced. For instance, the articles can be made from a starting linearor branched PHA by reactive extrusion, in which the thermolysis and thebranching are done in-process, and where portions of the extrusiontemperature and the residence time are sufficient for the thermolysisand branching steps. These steps can then be followed immediately byeither extrusion of the PHA in pellet form (for production at anothertime into finished articles), or processing (such as by molding) of thebranched PHA into finished articles immediately.

The specific examples below are to be construed as merely illustrative,and not limitative of the remainder of the disclosure in any waywhatsoever. Without further elaboration, it is believed that one skilledin the art can, based on the description herein, utilize the presentinvention to its fullest extent. All publications cited herein arehereby incorporated by reference in their entirety.

EXAMPLES Testing Methods Measurement of Molecular Weight of Polymers

Molecular weight (either weight-average molecular weight (Mw) ornumber-average molecular weight (Mn)) of PHA is estimated by gelpermeation chromatography (GPC) using, e.g., a Waters Alliance HPLCSystem equipped with a refractive index detector. The column set is, forexample, a series of three PLGel 10 micrometer Mixed-B (Polymer Labs,Amherst, Mass.) columns with chloroform as mobile phase pumped at 1ml/min. The column set is calibrated with narrow distributionpolystyrene standards.

The PHA sample is dissolved in chloroform at a concentration of 2.0mg/ml at 60C. The sample is filtered with a 0.2 micrometer Teflonsyringe filter. A 50 microliter injection volume is used for theanalysis.

The chromatogram is analyzed with, for example, Waters Empower GPCAnalysis software. Molecular weights and PD are reported as polystyreneequivalent molecular weights.

Measurement of Polydispersity (PD)

The polydispersity index (PD, or PDI) is a measure of the distributionof molecular mass in (individual molecular masses) a given polymersample. It is calculated from the weight average molecular weight (Mw)divided by the number average molecular weight (Mn). The PD has a valuealways greater than 1, but as the polymer chains approach uniform chainlength, the PDI approaches unity (i.e., 1). It is therefore useful as ameasure of the distribution of chain lengths in a polymer sample.

Measuring G′ Using Torsional Melt Rheometry

Torsional rheometry can be used to measure the melt strength of apolymer. For purposes of simplicity, G′ will be used herein, measured atan imposed frequency of 0.25 rad/s as a measure of “melt strength”(unless otherwise indicated). Higher G′ translates to higher meltstrength.

All oscillatory rheology measurements are performed using a TAInstruments AR2000 rheometer employing a strain amplitude of 1%. First,dry pellets (or powder) are molded into 25 mm diameter discs that areabout 1200 microns in thickness. The disc specimens are molded in acompression molder set at about 165° C., with the molding time of about30 seconds. These molded discs are then placed in between the 25 mmparallel plates of the AR2000 rheometer at 160° C. A gap of 800-900microns is used, depending on the normal forces exerted by the polymer.The melt density of PHB is determined to be about 1.10 g/cm³ at 160° C.;this value is used in all the calculations. Specifically, the specimendisc is loaded on the parallel plate rheometer set at 160° C.

During the frequency sweep performed at 160° C., the following data arecollected as a function of measurement frequency: |η*| or complexviscosity, G′ or elastic modulus (elastic or solid-like contribution tothe viscosity) and G″ or loss modulus (viscous or liquid-likecontribution to the viscosity).

As used herein, G′ measured at an imposed frequency of 0.25 rad/s(unless otherwise indicated) is used as a measure of “melt strength.”Higher G′ translates to higher melt strength.

Example 1 Effect of Heat Treatment on Branching

Experiments were carried out to demonstrate the effect of thethermolysis step on the branching ofpoly(3-hydroxybutyrate-co-8%-3-hydroxyvalerate) (“PHBV8”) witht-butylperoxybenzoate (TBPB; from R.T. Vanderbilt Co., Norwalk Colo.Specifically, PHBV8 was thermolysed by heating at 210° C. in a singlescrew extruder (1 inch screw diameter, Welex Inc, Blue Bell, Pa.)operating at 40 RPM, resulting an average residence time of about 1.6minutes, which reduced its weight average molecular weight to 263,000from 458,000. The thermolysed PHBV8 as well as the original PHBV8 werethen each mixed with 0%, 0.15%, or 0.30% (by weight) of the peroxideTBPB, and fed into a single screw extruder operating at 165° C. and 30RPM, with an average residence time of about 2 minutes. At 165° C., CPKhas a half-life of about 0.3 minutes. The molecular weights of thebranched polymers obtained from the extruder were determined by GPC andshown in Table 1, below. Mw/Mw,0 is the molecular weight of theperoxide-treated polymer, divided by the Mw of the correspondingstarting or initial polymer that was not peroxide-treated.

TABLE 1 Effect of thermolysis on molecular weights of branched PHApolymers. Wt % Peroxide Peroxide Thermolysed Mw PD Mw/Mw, o TBPB 0 Y263,000 2.4 1.0 TBPB 0.15 Y 343,000 3.2 1.3 TBPB 0.30 Y 525,000 4.1 2.0TBPB 0 N 458,000 2.3 1.0 TBPB 0.15 N 536,000 2.9 1.2 TBPB 0.30 N 616,0004.4 1.3 TBPB 0.45 N 666,000 3.9 1.5

In both cases, increases in branching are observed as indicated by theincrease in the weight average molecular weight ratio, Mw/Mw,o. Clearly,the increase in molecular weight, and hence the amount of branching, isgreater for the thermolysed PHBV8 as indicated by the greater values ofMw/Mw,o at comparable levels of peroxide.

Example 2 Branching of PHA Polymers with TAEC

Branched PHAs were prepared usingpoly(3-hydroxybutyrate-co-8%-3-hydroxyvalerate) (“PHBV8”) andpoly(3-hydroxybutyrate-co-7%-4-hydroxybutyrate) (“PHB7”) as the startingmaterials, and branching them with t-amylperoxy-2-ethylhexylcarbonate(TAEC). As measured by GPC, the PHBV8 starting polymer had a weightaverage molecular weight of 734,850 and a number average molecularweight of 288,571 g/mol. The PHB7 starting polymer had a weight averagemolecular weight of 505,000 and a number average molecular weight of207,000 g/mol.

The PHBV8 and PHB7 were thermolysed by heating at 210° C. in a singlescrew extruder (1 inch screw diameter, Welex Inc, Blue Bell, Pa.)operating at 40 RPM, resulting an average residence time of about 1.6minutes. The thermolysed PHBV8 had a weight average molecular weight ofabout 220,000 Daltons and a polydispersity (PD) index of about 2.7,while the PHB7 was 214,000 Daltons and had a PD of 8.4. Subsequently,the PHBV8 was mixed with 0.30, 0.45, or 0.60 wt % and the PHB7 was mixedwith 0.40 wt % t-amylperoxy-2-ethylhexylcarbonate (TAEC). The mixtureswere fed into the same extruder operating at 165° C. and 30 RPM, havingan average residence time of about 2 minutes. TAEC has a half-life ofabout 0.3 minutes at 165° C. The molecular weights of the branchedpolymers obtained from the extruder were determined by gel permeationchromatography (GPC). Also calculated were the ratios of the weightaverage molecular weight of the branched PHA over the weight averagemolecular weight of the starting PHA. This data is provided in Table 2,below.

TABLE 2 Molecular Weights of PHA Polymers Thermolysed and Branched withTAEC. Polymer Wt % TAEC Mw PD Mw/Mw, o PHBV8 0 220,000 2.7 1.0 PHBV80.30 380,000 3.6 1.7 PHBV8 0.45 600,000 5.7 2.8 PHBV8 0.60 600,000 8.42.8 PHB7 0 214,000 2.6 1.0 PHB7 0.40 475,000 4.0 2.2

Unexpectedly, the branched polymer obtained from the mixture containing0.30 wt % TAEC had a weight average molecular weight of about 380,000Daltons and a polydispersity index of about 3.8. The branched polymerobtained from the mixture containing 0.45 wt % TAEC had a weight averagemolecular weight of about 600,000 Daltons and a polydispersity index ofabout 5.8. The branched polymer obtained from the mixture containing0.60 wt % TAEC had a weight average molecular weight of about 600,000Daltons and a polydispersity index of about 7.0. The column Mw/Mw,oshows the normalized increase in weight average molecular weight.

These results show that branching occurred, as evidenced by the increasein both the weight average molecular weight and polydispersity.Additionally, the level of molecular weight increase (Mw/Mw,o) issimilar for PHBV8 and PHB7 at comparable levels of TAEC, indicating thatthe co-monomer component has a negligible effect on the branchingreaction.

Example 3 Branching of PHA Polymers with TBPB and CPK

Other initiators were tested for their capability in inducing branching.Poly(3-hydroxy butyrate-co-11%-4-hydroxybutyrate) (PHB11) with a weightaverage molecular weight of 559,000 and a number average molecularweight of 278,000 was thermolysed under similar conditions as in Example1, to a weight average molecular weight of about 270,000 Daltons. Thepolymer was then branched with t-butylperoxybenzoate (TBPB; Varox TBPBfrom R.T. Vanderbilt Co., Norwalk, Conn.) and1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane (CPK; Varox 231 fromR.T. Vanderbilt Co., Norwalk, Conn.) at levels of 0.15 and 0.30 wt %.The extruder was maintained at 165° C. For CPK, the extruder wasoperated at 60 RPM with an average residence time of about 1 minute. At165° C., the half-life of CPK is about 0.3 minutes. For TBPB, theextruder was operated at 10 RPM with an average residence time of about4.5 minutes. At 165° C., the half-life of TBPB is about 1 minute. Themolecular weights of the branched polymers obtained from the extruderwere determined by GPC as shown in Table 3, below.

TABLE 3 Molecular weights of PHA Polymers Thermolysed and Branched withTBPB and CPK. Peroxide Wt % Peroxide Mw PD Mw/Mw, o TBPB 0 270,000 2.01.0 TBPB 0.15 489,000 2.8 1.8 TBPB 0.30 537,000 3.2 2.0 CPK 0 267,0002.6 1.0 CPK 0.15 315,000 2.6 1.2 CPK 0.30 382,000 2.6 1.4

When CPK was used as an initiator, the branched polymer obtained fromthermolysed PHB11 had a weight average molecular weight up to 2.0 timesas high as the starting polymer with TBPB peroxide. Similarly, CPKperoxide effectively increases the weight average molecular weight.

These results show that various peroxides can be used effectively if thedecomposition temperature and residence time for the branching reactionis commensurate with the rate of decomposition (half-life) of theperoxide.

Example 4 Effect of Branching on Melt Strength

Rheological measurements were carried out to determine the effect ofbranching on the melt strength of PHA copolymer. The samples of PHB11from Example 3 that were branched using TBPB peroxide were analyzedfurther, by dynamic melt rheology at 160° C. using a Rheometrics RSAparallel plate rheometer. The (G′) measured at 0.25 sec⁻¹ was used an ameasure of melt strenght of the branched polymer. The results are shownin Table 5, below.

TABLE 5 Effect of Branching on Melt Strength. Sample Mw PD Mw/Mw, o G'(Pa) 1 270,000 2.0 1.0 19.3 2 489,000 2.8 1.8 2094 3 537,000 3.2 2.03752

The branched polymer obtained from the mixture without TBPB peroxide hada melt strength of about 19 Pa at 0.25 rad/s. The branched polymerobtained from the mixture containing 0.15 wt % TBPB had a melt strengthof nearly 2100. The branched polymer obtained from the mixturecontaining 0.30 wt % TBPB had a melt strength of about 3800 Meltstrength (G′) is another measure of polymer branching, and confirms thatthe polymer is being branched.

Other than in the examples herein, or unless otherwise expresslyspecified, all of the numerical ranges, amounts, values and percentages,such as those for amounts of materials, elemental contents, times andtemperatures of reaction, ratios of amounts, and others, in thefollowing portion of the specification and attached claims may be readas if prefaced by the word “about” even though the term “about” may notexpressly appear with the value, amount, or range. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains errornecessarily resulting from the standard deviation found in itsunderlying respective testing measurements. Furthermore, when numericalranges are set forth herein, these ranges are inclusive of the recitedrange end points (i.e., end points may be used). When percentages byweight are used herein, the numerical values reported are relative tothe total weight.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of I and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10. The terms “one,” “a,” or “an”as used herein are intended to include “at least one” or “one or more,”unless otherwise indicated.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

All of the features disclosed in this specification may be combined inany combination. Each feature disclosed in this specification may bereplaced by an alternative feature serving the same, equivalent, orsimilar purpose. Thus, unless expressly stated otherwise, each featuredisclosed is only an example of a generic series of equivalent orsimilar features.

From the above description, one skilled in the art can easily ascertainthe essential characteristics of the present invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Thus, other embodiments are also within the scope of thefollowing claims.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method of branching a starting biologically-producedpolyhydroxyalkanoate polymer (PHA), comprising the steps of: a)thermolysing the starting PHA to reduce its molecular weight between 25%and 75% from its starting molecular weight, and b) reacting thethermolyzed PHA from step a) with a branching agent, thereby forming abranched PHA, wherein the branching agent is a peroxide.
 2. A processfor producing a branched polyhydroxyalkanoate (PHA), comprising:providing an initial PHA; thermolysing the initial PHA to reduce itsmolecular weight and produce PHA with reactive ends, wherein thethermolysis is conducted at a temperature for a sufficient time that theweight average molecular weight of the PHA with reactive ends is fromabout 25% to about 75% of the weight average molecular weight of theinitial PHA; and treating the PHA with reactive ends with a branchingagent at a reactive temperature for a reaction time to provide forcross-linking between molecules of PHA with reactive ends, to produce abranched PHA; thereby producing a branched PHA, wherein the branchingagent is a peroxide.
 3. The method of claim 1, wherein the PHAthermolysed in step a) is linear.
 4. The method of claim 1, wherein thePHA thermolysed in step a) is branched.
 5. The method of claim 1,wherein the PHA molecular weight is reduced in step a) by at least 50%from its starting molecular weight.
 6. The method of claim 1, whereinthe PHA molecular weight is reduced in step a) by at least 40% from itsstarting molecular weight.
 7. The method of claim 1, wherein thethermolysing occurs at a temperature of 190° C. to 250° C.
 8. The methodof claim 1, wherein the thermolysing occurs at a temperature of 190° C.to 220° C.
 9. The method of claim 1, wherein the residence time forthermolysing occurs for 0.1 minutes to 1.6 minutes.
 10. The method ofclaim 1, wherein the thermolysing and reacting with a branching agentoccur in separate zones inside an extruder.
 11. The method of claim 1,wherein the peroxide is selected from: dicumyl peroxide,t-amyl-2-ethylhexyl peroxycarbonate, t-butyl-2-ethylhexylperoxycarbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-bis(t-butylperoxy)-2,5-dimethylhexane,2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoylperoxide, di-t-amyl peroxide, t-butyl cumyl peroxide,n-butyl-4,4-bis(t-butylperoxy)valerate,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)-cyclohexane,2,2-di(t-butylperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate,2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate,t-butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate,t-amylperoxybenzoate, di-t-butyldiperoxyphthalate,tert-butylperoxy-2-ethylhexylcarbonate,tert-amylperoxy-2-ethylhexylcarbonate, andn-butyl-4,4-di-(tert-butylperoxy)valerate.
 12. (canceled)
 13. The methodof claim 1, wherein the concentration of branching agent is between0.001 to 0.5% by weight of the PHA or between 0.01 to 0.1% by weight ofthe PHA.
 14. (canceled)
 15. The method of claim 1, wherein the meltstrength (G′) of the branched PHA is greater than the melt strength ofthe starting PHA as measured at 0.25 rad/sec at 160° C.
 16. The methodof claim 15, wherein the melt strength of the branched PHA is at leasttwice to about 20 times that of the starting PHA.
 17. The method ofclaim 15, wherein the melt strength of the branched PHA is at least fiveto 15 times that of the starting PHA.
 18. The method of claim 1, whereinthe branched PHA has a molecular weight greater than the starting PHA.19. The method of claim 1, wherein, the biologically-producedpolyhydroxyalkanoate polymer is a poly(3-hydroxybutyrate) homopolymer, apoly(3-hydroxybutyrate-co-4-hydroxybutyrate), apoly(3-hydroxybutyrate-co-3-hydroxyvalerate), apoly(3-hydroxybutyrate-co-5-hydroxyvalerate), or apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate; a poly(3-hydroxybutyrate)homopolymer, a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with 5% to15% 4-hydroxybutyrate content, apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 5% to 22%3-hydroxyvalerate content, apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with 5% to 15%5-hydroxyvalerate content, or apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with 3% to 15%3-hydroxyhexanoate content; a polymer blend of a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate); a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate); a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate); a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate); a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate); a polymer blend of a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content; a) a poly(3-hydroxybutyrate) homopolymerblended with b) a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5%to 22% 3-hydroxyvalerate content; a) a poly(3-hydroxybutyrate)homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content; a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content; a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content or a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content; a polymer blend of a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) and the weight of polymera) is 5% to 95% of the combined weight of polymer a) and polymer b); a)a poly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) and the weight of polymera) is 5% to 95% of the combined weight of polymer a) and polymer b); a)a poly(3-hydroxybutyrate) homopolymer blended to with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and the weight of polymera) is 5% to 95% of the and polymer b a aoly(3-hydroxybutyrate-co-4-hydroxbutyrate) blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) and the weight of polymera) is 5% to 95% of the combined weight of polymer a) and polymer b); a)a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blended with b) apoly(3-hydroxbutrate-co-3-hdroxhexanoate) and the weight of polymer a)is 5% to 95% of the combined weight of polymer a) and polymer b); or a)a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and the weight of polymera) is 5% to 95% of the combined weight of polymer a) and polymer b);wherein the weight of polymer a) is 20% to 60% of the combined weight ofpolymer a) and polymer b) and the weight of polymer b) is 40% to 80% ofthe combined weight of polymer a) and polymer b); a polymer blend of a)poly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content; a) a poly(3-hydroxybutyrate) homopolymerblended with b) a poly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a20% to 50% 5-hydroxyvalerate content; a) a poly(3-hydroxybutyrate)homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content; a)poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content; a)poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate content; a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content; a) apoly(3-hydroxybutyrate-co-3-hydroxvvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b)poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content; a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b) apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate content; a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content; a) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content; a) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate; or a) a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)with a 3% to 15% 3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content; a polymer blend of a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate) homopolymer blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a copolymer blend ofa) a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b)poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b);a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b)poly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate and the weigt of polymer a) is 5% to 95% of thecombined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 5% to 15%4-hydroxybutyrate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a copolymer blend ofa) a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b)poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b) apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate and the weight of polymer a) is 5% to 95% of thecombined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 5% to 22%3-hydroxyvalerate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a copolymer blend ofa) a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20-50%4-hydroxybutyrate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); a) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate and the weight of polymer a) is 5% to 95% of thecombined weight of polymer a) and polymer b); or a) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 3% to 15%3-hydroxyhexanoate content blended with b) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 5%-50%3-hydroxyhexanoate content and the weight of polymer a) is 5% to 95% ofthe combined weight of polymer a) and polymer b); wherein the weight ofpolymer a) is 20% to 60% of the combined weight of polymer a) andpolymer b) and the weight of polymer b is 40% to 80% of the combinedweight of polymer a) and polymer b). 20-27. (canceled)
 28. The method ofclaim 1, wherein the biologically-produced polyhydroxyalkanoate isfurther blended with polymer c) apoly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a 20% to 50%4-hydroxybutyrate content; apoly(3-hydroxybutyrate-co-5-hydroxyvalerate) with a 20% to 50%5-hydroxyvalerate content or c) apoly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a 5% to 50%3-hydroxyhexanoate content. 29-30. (canceled)
 31. The method of claim28, wherein the weight of polymer c) is 5% to 95% of the combinedpolymer weight of polymer a), polymer b) and polymer c) or the weight ofpolymer c is 5% to 40% of the combined polymer weight of polymer a),polymer b) and polymer c).
 32. (canceled)
 33. An article comprising thebranched polymer made by the method of claim
 1. 34. The article of claim33, wherein the article is a utensil, tub, bowl, lid, cup lid, yogurtcup, container, bottle, bottle-like containers, or other container-typeitems.
 35. A thermoformed article comprising a branched PHA produced bybranching a starting polyhydroxyalkanoate polymer (PHA), comprising thesteps of: a) thermolysing the starting PHA to reduce its molecularweight between 25% and 75% from its starting molecular weight, b)reacting the thermolysed PHA from step a) with a branching agent at atemperature above the decomposition temperature of the branching agent,thereby forming a branched PHA, and c) extruding and thermoforming thebranched PHA into an article.
 36. The article of claim 35, wherein thearticle is a utensil, tub, bowl, lid, cup lid, yogurt cup, container,bottle, bottle-like containers, or other container-type items. 37.(canceled)
 38. An article comprising the branched polymer of claim 19.39. The article of claim 38, wherein the article is thermoformed.